### Virtual Method

# Gio InputStream read_async

#### Declaration [src]

    void
    read_async (
      GInputStream* stream,
      void* buffer,
      gsize count,
      int io_priority,
      GCancellable* cancellable,
      GAsyncReadyCallback callback,
      gpointer user_data
    )

#### Description [src]

Request an asynchronous read of `count` bytes from the stream into the buffer starting at `buffer`. When the operation is finished `callback` will be called. You can then call `g_input_stream_read_finish()` to get the result of the operation.

During an async request no other sync and async calls are allowed on `stream`, and will result in `G_IO_ERROR_PENDING` errors.

A value of `count` larger than `G_MAXSSIZE` will cause a `G_IO_ERROR_INVALID_ARGUMENT` error.

On success, the number of bytes read into the buffer will be passed to the callback. It is not an error if this is not the same as the requested size, as it can happen e.g. near the end of a file, but generally we try to read as many bytes as requested. Zero is returned on end of file (or if `count` is zero), but never otherwise.

Any outstanding i/o request with higher priority (lower numerical value) will be executed before an outstanding request with lower priority. Default priority is `G_PRIORITY_DEFAULT`.

The asynchronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one you must override all.

#### Parameters

`buffer`

  Type: An array of `guint8`

  a buffer to read data into (which should be at least count bytes long).

  The argument will be set by the function.
  The argument can be set to `NULL` by the virtual function.
  The length of the array is specified in the `count` argument.
  The returned data is owned by the instance.

`count`

  Type: `gsize`

  The number of bytes that will be read from the stream.

`io_priority`

  Type: `int`

  The I/O priority of the request.

`cancellable`

  Type: `GCancellable`

  Optional `GCancellable` object, `NULL` to ignore.

  The argument can be `NULL`.
  The data is owned by the caller of the method.

`callback`

  Type: `GAsyncReadyCallback`

  A `GAsyncReadyCallback` to call when the request is satisfied.

`user_data`

  Type: `gpointer`

  The data to pass to callback function.

  The argument can be `NULL`.
  The data is owned by the caller of the method.